1. Field of the Invention
The present invention relates to an apparatus for transferring objects from a first region to a second region, the first and second regions having differing atmospheric environments. In particular, the present invention relates to an apparatus that enables movement of a series of objects into and out of a region having a different atmospheric condition while minimizing the escape of the atmosphere of that region. The United States Government has rights in this invention pursuant to Contract No. DE-AC09-89SR18035 between the U.S. Department of Energy and Westinghouse Savannah River Company.
2. Discussion of Background
There are many instances where two regions are separated by a barrier but a passageway is formed in the barrier so that objects or people can pass through. If the atmospheric conditions--temperature, pressure, atmospheric constituents--of one region are different from those of the other, movement of objects or individuals may be controlled to minimize, if not avoid, the blending of the atmospheric conditions of the two zones.
The simplest example of this situation is a door that can be closed after a person enters or leaves a building that is heated or air conditioned. The door may be made more elaborate to assure that the loss of energy associated with heating and air conditioning is minimized: the door may be self closing or may be a revolving door.
A more complex type of passageway is an airlock which is in effect a room between two regions wherein the atmospheric conditions are adjusted to match the region to which the object or person is going from that of the region whence it comes.
The degree of difference between the two regions dictates in part the level of effort required to limit or prevent blending of atmospheres.
In manufacturing and testing, there are processes that require materials and objects to be passed between regions of differing temperatures or pressures, or between regions having atmospheres of different compositions. In some applications, it is sufficient to limit the tree movement of atmosphere between two regions, while in other applications it is important to prevent cross-contamination between the regions. Similar situations are encountered in space and undersea exploration, in air-supported structures such as athletic stadiums, and in the construction industry when temporary air-supported formwork is used.
Many manufacturing processes run continuously, with materials being processed in generally steady streams rather than in discrete batches. Because of the need for repeated cycling, an airlock is inherently a batch device and unsuitable for continuous processes. If airlocks are used in such processes, materials or parts must be collected into batches for passage through the airlock, then dispersed again on its further side. Thus, airlocks are bottlenecks in any otherwise continuous or nearly continuous process.
Moving objects generally, whether between two regions or otherwise, usually entails a conveyor. These might be used in combination with other structures for controlling the movement of material. For example, conveyors with outwardly-projecting flights are used for transporting particulate materials. Abel (U.S. Pat. No. 5,049,007) describes such a conveyor, wherein the free edges of the flights seal against a planar sealing surface located above and parallel to the conveyor belt. In the metering surge bin airlock disclosed by Hamilton (U.S. Pat. No. 4,122,003), the flights are attached to a conveyor belt that extends from a surge bin to a head drum. An arcuate member is disposed about the head drum, such that the inner surface of the member forms a seal with the material carded by the conveyor so that air cannot flow between the material and the member. These devices are not suitable for transporting items between regions of substantially differing atmospheres. Both devices release the transported materials to fall into a container, pneumatic separator or the like. Fragile objects may be damaged by the impact of the fall. Also, it is difficult or impossible to track individual objects passing through such a device.
Rotary devices are also used for transferring objects or particulate materials between two regions. Revolving doors are, of course, well known for controlling the flow of air coming through the door in both directions. A revolving door consists of a curved housing with a vertical axis and openings on opposite sides. Vanes with the axis lying in the same plane radiate from the axis and seal against the inner surfaces of the cylinder as they revolve about that axis. When the vanes are fixed in position, flow stops completely. Magnani (U.S. Pat. No. 4,225,900) provides a safety device that makes possible the normal flow of persons past a fixed revolving door. Douglas (U.S. Pat. No. 4,205,216) provides a laser welding system that includes a housing for a welding station and a revolving door-type turntable for moving workpieces into and out of the housing.
Rotary feeders with generally horizontal axes are also known. In these devices, materials enter the feeder through an inlet and are transported to an outlet by the revolving vanes, as in the devices shown by Fischer (U.S. Pat. No. 4,179,043) and Ruiz (U.S. Pat. No. 3,556,355). Thompson (U.S. Pat. No. 2,551,981) provides a conveyor mechanism with two such rotary feeders, the first receiving material at the inlet and dropping the material onto a conveyor, the second receiving material that is dropped from the conveyor and discharging the material at the outlet.
In all of these rotary devices, materials are transported through a stationary shell by the action of the revolving vanes. Typically, materials fall into the inlet, are moved to the outlet by the vanes, and fall out of the device at the outlet. As in the conveyors described above, materials are scrambled by passage through the device, and fragile objects may be damaged by the impact of the fall.
An apparatus that permits more nearly continuous flow of materials and objects therethrough, while substantially preventing different atmospheres on its opposite sides from mixing or while maintaining a pressure difference between two regions, would be useful in many manufacturing and testing processes. Preferably, the orientation and relative position of materials and objects would be maintained during passage through the apparatus.